69,787 research outputs found
Scattering Amplitudes of Massive N=2 Gauge Theories in Three Dimensions
No full textWe study the scattering amplitudes of mass-deformed Chern-Simons theories and Yang-Mills-Chern-Simons theories with N=2 supersymmetry in three dimensions. In particular, we derive the on-shell supersymmetry algebras which underlie the scattering matrices of these theories. We then compute various 3 and 4-point on-shell tree-level amplitudes in these theories. For the mass-deformed Chern-Simons theory, odd-point amplitudes vanish and we find that all of the 4-point amplitudes can be encoded elegantly in superamplitudes. For the Yang-Mills-Chern-Simons theory, we obtain all of the 4-point tree-level amplitudes using a combination of perturbative techniques and algebraic constraints and we comment on difficulties related to computing amplitudes with external gauge fields using Feynman diagrams. Finally, we propose a BCFW recursion relation for mass-deformed theories in three dimensions and discuss the applicability of this proposal to mass-deformed N=2 theories
Mechanism of Benzene Hydroxylation on Tri-Iron Oxo-Centered Cluster-Based Metal-Organic Frameworks
No full textHigh-valent Fe(IV)-oxo species derived upon reactions of N2O with Fe(II) centers & horbar;embedded in the framework of tri-iron oxo-centered-based metal-organic frameworks (MOFs)& horbar; selectively affect the conversion of benzene-to-phenol via electrophilic addition to arene C-H bonds akin to oxygen transfer mechanisms in the P450 enzyme. The Fe(II) species identified by M & ouml;ssbauer spectroscopy can be titrated in situ by the addition of NO to completely suppress benzene oxidation, verifying the relevance of Fe(II) centers. Observed inverse kinetic isotope effects in benzene hydroxylation preclude the involvement of H atom transfer steps from benzene to the Fe(IV)-oxo species and instead suggest that the electrophilic iron-oxo group adds to an sp(2) carbon of benzene, resulting in a change in the hybridization from sp(2)-to-sp(3). These mechanistic postulates are affirmed in Kohn-Sham density functional calculations, which predict lower barriers for additive mechanisms for arene oxidation than H atom abstraction steps. The calculations show that the reaction proceeds on the pentadectet spin surface and that a non-innocent ligand participates in the transfer of the H atom. Following precedent literature which demonstrates that these Fe(IV)-oxo species react with C-H bonds in alkanes via hydrogen atom abstraction to form alcohols, it appears that iron(IV)-oxo species in MOFs exhibit duality in their reactions with inert hydrocarbon substrates akin to enzymes & horbar;if the C-H bonds are in saturated aliphatic hydrocarbons, then activation occurs via hydrogen abstraction, while if the C-H bonds are aromatic, then activation occurs by addition rearrangement
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A probabilistic assessment of sea level variations within the Last Interglacial stage
No full textThe Last Interglacial (LIG) stage (ca. 130–115 ka) provides a relatively recent example of a world with both poles characterized by greater-than- Holocene temperatures similar to those expected later in this century under a range of greenhouse gas emission scenarios. Previous analyses inferred that LIG mean global sea level (GSL) peaked 6–9 m higher than today (Kopp et al. 2009; Dutton & Lambeck 2012). Here, we extend our earlier work to perform a probabilistic assessment of sea level variability within the LIG highstand. Using the terminology for probability employed in the Intergovernmental Panel on Climate Change (IPCC) assessment reports, we find it extremely likely (95% probability) that the paleo-sea level record allows resolution of at least two intra-LIG sea level peaks and likely (67% probability) that the magnitude of low-to-high swings exceeded 4 m. Moreover, it is likely that there was a period during the LIG in which GSL rose at a 1000-year average rate exceeding 3 m/ky, but unlikely (33% probability) that the rate exceeded 7 m/ky and extremely unlikely (5% probability) that it exceeded 11 m/ky. These rate estimates can provide insight into rates of Greenland and/or Antarctic melt under climate conditions partially analogous to those expected in the twenty- first century.This is the authors’ preprint version of the manuscript: 23 January 2013. Originally submitted 18 September 2012. Accepted for publication in Geophysical Journal International, published by Oxford University Press.Peer reviewe
DNA Mutations via Chern–Simons Currents
No full textWe test the validity of a possible schematization of DNA structure and dynamics based on the Chern–Simons theory, that is a topological field theory mostly considered in the context of effective gravity theories. By means of the expectation value of the Wilson Loop, derived from this analogue gravity approach, we find the point-like curvature of genomic strings in KRAS human gene and COVID-19 sequences, correlating this curvature with the genetic mutations. The point-like curvature profile, obtained by means of the Chern–Simons currents, can be used to infer the position of the given mutations within the genetic string. Generally, mutations take place in the highest Chern–Simons current gradient locations and subsequent mutated sequences appear to have a smoother curvature than the initial ones, in agreement with a free energy minimization argument
Trasmissible Spongiform Encephalopathies
No full textProtein folding and misfolding, relevance to disease and function / Massimi Stefani --
Alzheimer's disease / Charlotte E. Teunissen and Tischa M. van der Cammen --
Improving Cholinergic Transmission --
Cholinergic transmission and acetylcholine release enhancers / Pierre Francotte, Pascal de Tullio and Bernard Pirotte --
AChE and its inhibition / Jure Stojan --
AChE inhibitors and their clinical assessment / Pierre Francotte, Pascal de Tullio and Bernard Pirotte --
Reduction in plaque formation / Christian Czech, Helmut Jacobsen and Celine Adessi --
Non-steroidal anti-inflammatory drugs (NSAIDs) / Bruno P. Imbimbo and Francesca Speroni --
3-hydroxy-3-methyl-glutaryl-coenzyme reductase inhibitors / Dario Cattaneo --
A' polymerization reduction / Harry LeVine III and Corrine E. Augelli-Szafran --
Carbonic anhydrase activators as potential anti-Alzheimer's disease agents / Claudiu T. Supuran and Andrea Scozzafava --
Detection and reduction of neurofibrillary lesions / Jeff Kuret --
Protein misfolding in Alzheimer disease : pathogenic or protective? / Rudy J. Castellani ... [et al.] --
Enhancement of brain retinoic acid levels / Ann B. Goodman ... [et al.] --
Parkinson's disease : what is it? what causes it? and how can it be cured? / Tom Foltynie, Andrew W. Michell and Roger A. Barker --
Restoring dopamine levels / Nuno Palma .. [et al.] --
Huntington's disease / Claire-Anne Gutekunst and Fran Norflus --
Amyotrophic lateral sclerosis (motor neuron disease) / Teresa Sanelli ... [et al.] --
Transmissible spongiform encephalopathies (TSEs) / Michael D. Geschwind and Giuseppe Legname --
Overview / H. John Smith, Claire Simons and Robert D.E. Sewell
Multiple membranes in M-theory
No full textJB acknowledges support from the U.S. National Science Foundation, grant NSF-PHY-0910467. NL was supported in part by STFC grant ST/G000395/1. CP is supported by the U.S. Department of Energy under grant DE-FG02-96ER40959
Did I turn off the gas? Reality monitoring of everyday actions.
No full textFailing to remember whether we performed, or merely imagined performing, an everyday action can occasionally be inconvenient but, in some circumstances, can have potentially dangerous consequences. In this fMRI study, we investigated brain activity patterns, and objective and subjective behavioral measures, associated with recollecting such everyday actions. We used an ecologically-valid 'reality monitoring' paradigm in which participants performed, or imagined performing, specified actions with real objects drawn from one of two boxes. Lateral brain areas, including prefrontal cortex, were active when participants recollected both the actions that had been associated with objects and the locations from which they had been drawn, consistent with a general role in source recollection. By contrast, medial prefrontal and motor regions made more specific contributions, with supplementary motor cortex activity associated with recollection decisions about actions but not locations, and medial prefrontal cortex exhibiting greater activity when remembering performed rather than imagined actions. The results support a theoretical interpretation of reality monitoring that entails the fine-grained discrimination between multiple forms of internally- and externally-generated information
Chern-Simons theory and S-duality
No full textWe study S-dualities in analytically continued SL(2) Chern-Simons theory on a 3-manifold M. By realizing Chern-Simons theory via a compactification of a 6d five-brane theory on M, various objects and symmetries in Chern-Simons theory become related to objects and operations in dual 2d, 3d, and 4d theories. For example, the space of flat SL(2, C ) connections on M is identified with the space of supersymmetric vacua in a dual 3d gauge theory. The hidden symmetry h → -4π^2/h of SL(2) Chern-Simons theory can be identified as the S-duality transformation of N=4 super-Yang-Mills theory (obtained by compactifying the five-brane theory on a torus); whereas the mapping class group action in Chern-Simons theory on a three-manifold M with boundary C is realized as S-duality in 4d N=2 super-Yang-Mills theory associated with the Riemann surface C. We illustrate these symmetries by considering simple examples of 3-manifolds that include knot complements and punctured torus bundles, on the one hand, and mapping cylinders associated with mapping class group transformations, on the other. A generalization of mapping class group actions further allows us to study the transformations between several distinguished coordinate systems on the phase space of Chern-Simons theory, the SL(2) Hitchin moduli space
Topics in Supersymmetry Breaking and Gauge/Gravity Dualities
No full textThe thesis covers two topics in string theory and quantum field theory. First, we realize metastable vacua in various supersymmetric gauge theories. Specifically, we consider the Coulomb branch of any N = 2 supersymmetric gauge theory, and perturb it by a superpotential and engineer a metastable vacuum at a point. We also study its relation to Kahler normal coordinates and Fayet-Iliopoulos terms. Having studied the metastable construction, we apply this to general gauge mediation. We show how to compute the current correlators when the hidden sector is strongly coupled in specific examples.
Next, we consider gauge/gravity dualities. We apply dualities to the investigation of various strongly coupled field theories. In one example, we construct M-theory supergravity solutions with the nonrelativistic Schroedinger symmetry starting from the warped AdS_5 metric with N = 1 supersymmetry. We impose that the lightlike direction is compact by making it a nontrivial U(1) bundle over the compact space. In another example, we show that, in a gravity theory with a Chern-Simons coupling, the Reissner-Nordstrom black hole in anti-de Sitter space is unstable depending on the value of the Chern-Simons coupling. The analysis suggests that the final configuration is likely to be a spatially modulated phase.</p
A note on amplitudes in N=6 superconformal Chern-Simons theory
No full textThis is the accepted version of an article subsequently published in Journal of High Energy Physics July 2012, 2012:160. The original publication is available at www.springerlink.com http://link.springer.com/article/10.1007%2FJHEP07%282012%29160This version deposited to arXiv 30-07-12 arXiv:1205.6705v3 [hep-th
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